1. Field of the Invention
This invention relates to the field of digital interfaces, and particularly to single-wire digital interfaces.
2. Description of the Related Art
A digital interface comprises circuitry designed to receive and buffer digital data, which is then made available to other circuitry. A common “3-wire” digital interface employs three inputs: DATA, CLK, and LOAD. The DATA and CLK inputs receive data and clock signals, respectively. The logic value of a data bit entered into the interface is determined by the voltage on the DATA input when the clock signal either rises or falls. The signal received at the LOAD input determines when a data word comprising a group of just-entered data bits is valid.
In some applications, a single input or “single-wire” digital interface may be desirable, such as when there are limitations on the number of available I/O pins on an integrated circuit (IC), the number of wires available to connect to an IC, or the number of drivers available to drive the interface. A single-wire interface needs to combine the functions of all three wires of a 3-wire interface. One possible single-wire approach is disclosed in U.S. Pat. No. 5,210,846 to Lee. Here, a single wire is used for bidirectional communication between a single host and either a single or multiple slave devices. The host starts communication by pulling the wire low and leaving it low for a short time t1. To write a 0, the host keeps the wire low after time t1. To write a 1, the host pulls the wire high after time t1. To read, the host releases control of the wire after time t1 and allows the slave to pull it low to send a 0, or leave it floating; if the slave leaves it floating then an external resistor pulls the wire high to send a 1. After a minimum predefined time t2 after time t1, the host can pull the wire high to prepare for the next communication bit. A command word at the start of each transfer defines the transfer type.
However, Lee's system requires a large number of components, and therefore may require an unacceptably large amount of space on an IC die and consume an excessive amount of current.